[llvm] [utils][UpdateLLCTestChecks] Add MIR support to update_llc_test_checks.py. (PR #164965)

[Alexander Richardson via llvm-commits]

arichardson wrote:

> Maybe naive question, but for your scenario, can you run just the passes you need, on MIR? I.e you could start with the pattern that you expect to be undone, and not rely on the earlier pass producing it. You'd also not need this change then.
> 
> ... which would avoid teasing the sentiments in this thread:
> 
> https://discourse.llvm.org/t/rfc-llvm-ai-tool-policy-start-small-no-slop/88476
> 
> (I'm assuming @arichardson's lgtm means at least one person is ok with maintaining Claude's output here)

The reason I approved this is that the change looks trivial and I have had cases in the past where I wanted to test the llc output both after a specific pass (usually ISel) as well as the final assembly. Not having to have two tests that could get out of sync is quite nice there but of course you could also use manual check lines or add a MIR test.

https://github.com/llvm/llvm-project/pull/164965